The present invention relates to a resin composition comprising a polyphenylene sulfide (hereinafter referred to as PPS) and a fluorinated resin, particularly to a resin composition whereby the dimensional accuracy of a three-dimensional molded product obtainable by an injection molding method is remarkably improved.
PPS is known as a resin excellent in heat resistance, solvent resistance, electrical properties, mechanical strength, dimensional stability, flame retardancy, etc. and its applications include a material for parts of electrical and electronic appliances, a material for parts of automobiles, a material for parts of chemical equipments and material for other functional parts.
In majority of such applications, parts formed by an injection molding method are employed. However, the required properties are finely divided. For example, among parts which used to be processed by metal cutting processing etc., there are ones which are required to have particularly high dimensional accuracy, and it has been difficult to substitute PPS for them.
The reason has been such that PPS has a low polymerization degree and is usually combined with e.g. an inorganic filler or a fiber-reinforcing agent such as glass fibers or carbon fibers to have properties useful as an engineering plastic, but when it is injection-molded, a phenomenon is likely to occur wherein depending upon the direction of alignment of the fiber reinforcing material, the dimension of the molded product differs, whereby a predetermined dimensional accuracy tends to be hardly obtainable.
Further, when an inorganic filler which brings about no problem of the alignment direction, such as glass beads, zinc oxide or calcium carbonate, is incorporated to PPS, the problem of alignment of the filler at the time of injection molding, will be solved, but fluctuations among molding shots tend to be large, and the required dimensional accuracy can not be satisfied.
For example, in order to obtain high dimensional accuracy of a three-dimensional molded product, there is a proposal such that a composition comprising PPS and a certain specific silane-treated silica powder, is molded into a connector ferrule for optical fiber (JP-A-6-299072), or a composition having from 0.5 to 5 wt % of PPS blended to a tetrafluoroethylene (hereinafter referred to as TFE)/perfluoro(alkylvinyl ether) (hereinafter referred to as PAVE) copolymer (hereinafter referred to as PFA), is used for lining by a rotational molding method (JP-A-5-112690). However, such compositions are different in the compositional ratio from the composition of the present invention.
There are also a proposal to obtain a molded product having the dimensional stability in oil and abrasion resistance improved by insert molding a cylinder piston from a composition comprising specific amounts of PPS, a fluorinated resin, a spherical filler and a fibrous filler (JP-A-3-74681), a proposal to obtain a molded product made of a composition comprising PPS, a polyvinylidene fluoride (hereinafter referred to as PVDF) and a homopolymer or copolymer of TFE (JP-A-5-29520), and a proposal to improve the mutual dispersibility of PPS and a fluorinated resin in a composition comprising PPS, a fluorinated resin having a melting point of at most 320xc2x0 C. and an aminoalkoxy silane and thereby to improve the mechanical strength of its molded product (JP-A-8-53592). However, there is no disclosure as to whether or not a molded product having high dimensional accuracy can thereby be obtained.
An object of the present invention is to provide a resin composition comprising PPS, a fluorinated resin and further a filler, whereby a three-dimensional molded product having high dimensional accuracy, can be obtained by injection molding.
The present inventors have conducted a study diligently and as a result, they have found it possible to accomplish the above object by incorporating to PPS a specific amount of a fluorinated resin having a solidification temperature higher than PPS and thus have arrived at the present invention.
Namely, the present invention provides a resin composition which comprises the following (a) and the following (b) in a proportion of from 50 to 99.5 wt % of (a) and from 0.5 to 50 wt % of (b) in the total amount of (a) and (b). Further, it provides the above resin composition which further contains the following (c) in a ratio of more than 0 part by weight and not more than 250 parts by weight in the total amount per 100 parts by weight of the total amount of (a) and (b).
(a) a polyphenylene sulfide;
(b) a fluorinated resin having a solidification temperature (Tmc) of at least 237xc2x0 C. when cooled at a cooling rate of 10xc2x0 C./min after melting in a nitrogen atmosphere at 330xc2x0 C.; and
(c) at least one member selected from the group consisting of an organic reinforcing material, an inorganic reinforcing material and a filler.